The prior art is acquainted with control elements that can be manually operated and that are used to trigger a switching process for electrical or mechanical installations.
Known here in particular are control elements that take the form of a snap disk, where a snap disk is understood as element with discontinuous transition characteristics such that, when the control element is actuated, the application of an actuating force by the snap disk generates a switching stroke and a snapping motion is executed. In particular, this snapping reversal is perceived by the user haptically, or by touch, and the user can thereby recognize that the switching event has been successfully triggered.
In industrial applications, control elements in the form of switches and sensors are increasingly subject to new requirements with respect to resistance to external influences, particularly influences of a mechanical, chemical, or weather-specific nature.
The mechanical influences take the form of potential damage caused by foreign objects, which are in a position to scratch, abrade, or penetrate surfaces, and therefore to cause mechanical failure of the control element. When devices are used in many areas of industry, for example, the food, solar energy, and pharmaceutical industries, devices must fulfill the requirements of sealing class IP69k, which specifically demands that the devices withstand in undamaged condition cleansing with a jet of pressurized water, with a pressure in the range from 80 to 100 bar, and a water temperature of 80° C., where the jet spacing is from 100 to 150 mm. This means that high demands are placed on the stability and robustness of the control element and the device, as well as on the seal between the control element and the device.
Chemical influences caused by aggressive media used in the industrial field—for example, the food industry—to purify production lines and their environment also place high demands on the material to be used, since aggressive cleaning media are able to bite into the surface of devices and to cause corrosion, and thus to damage the devices and jeopardize their long-term reliability.
Included among weather-determined instances of damage to a control system are, for example, the missing or insufficient resistance of the employed materials with respect to ultraviolet radiation and ozone. A further problem area is posed by the tightness, temperature resistance, and resistance to change in temperature that are demanded of the control elements.
In addition to the material-technical requirements for the control element, the demand for a haptic perception of the switching event is of primary importance in providing a user-friendly control element. Upon actuation of a scanner this is defined by a tactile snapping movement, which is perceptible during the operation.
For example, DE 10 2004 004 136 B4 discloses a small electrical device with a snap disk made of plastic. DE 41 39554 A1 discloses a snap disk of sheet metal for use as a contact element for a switch, with an additional protective layer of plastic. Snap disks of metal are disadvantageous, however, in that they require a degree of freedom on the outer rim in order to permit the center of the snap disk to move. Metal snap disks therefore rest only on a wall or in a recess. If disks of this kind are firmly clamped, the snap disk stiffens into an inflexible structure, which can only be reformed through deformation. To permit a seal of the metal snap disks relative to the housing, additional sealing elements are required, like those known, for example, from DE 10 2006 010 811 A1.